The objective of this study was to investigate whether a diet rich in legumes are associated with oxidative stress among type 2 diabetic patients. In a randomized, controlled, crossover clinical trial, 31 type 2 diabetic patients were randomly assigned to receive 2 diets, each for a period of 8 weeks: (1) The legume-free therapeutic lifestyle change (TLC) diet and (2) the legume-based TLC diet. Both diets were similar except that 2 servings of red meat were replaced by different types of legumes 3 days per week in the legume-based TLC diet. Oxidative stress biomarkers were measured at baseline and after 8 weeks. Compared to the legume-free TLC diet, the legume-based TLC diet significantly decreased malondialdehyde (-0.22 versus -0.68 μmol/l; P=0.002), oxidized-LDL (-0.9 versus -2.3 mU/l; P=0.05) and increased nitric oxide (0.40 versus 0.96 mM/l; P=0.03) and catalase activity (1.2 versus 2.1 Iu/ml; P=0.05).